I've had this '86 truck for almost 20 years. When I first got it the front windshield leaked really bad. I know! Who ever heard of such! Amazingly I've done very well in stopping the leaks by caulking and recaulking and then caulking my caulking. Every once in awhile I would find that last nights rain did not soak the floors. I now have floor mats that catch all the leaks.

But the other week I noticed something that I had not caught before. Whenever I leave my wiper blades UP, the windshield doesn't leak. When I leave them down in the OFF position the windshield leaks. This is not a one off thing. It's repeatable.

How is this possible? I can't see the wiper blade pushing down on the windshield or the trim hard enough to make it leak. Has anyone else seen this?

 

Wiper blades route the water in the direction of the hole?

 

Yea so to get weird, you have 16 inch blades so 16 inches of surface area grabbing the whatever inches of rain coming down your windshield then the angle of your windshield wipers may be up or downwards so it takes said inches of surface area rain and routes it to said hole so 32 inches total of channeled rain could be flowing into the hole just ever so perfectly……..

but nonsense aside, yes they will take more water and concentrate it more while against the windshield rather than up or pulled up….

 

I had the same issue in my 87 suby GL, I just bought some wide electrical tape and went around the windshield, then I would
trim it so it almost looked like it wasn’t there, granted I had to replace every year or so but the car was super hard to get glass and a seal for some reason so I did what I had to do…..

 

That's a good thought that the wiper blades are funneling the water to a certain leak spot when they're in the down position. I may have to do some rain testing of mine own now.

 

with the wipers down, is it leaking on both sides, or just the passenger side?

Any chance the cowl is full of muck, and its coming in through the HVAC?

 

I had 2 water access point inside the passenger foot well. One on the firewall up high and one i believe just above the corner of the windshield. I could only find the fire wall as it was a small rust hole in the firewall under that crimp like horizontal seam. I removed the cowl and it looked like new and didn't even have any dirt or debris. I was not going to remove the chrome trim as I would never get it back in place. Kind of like you, I sealed the trim edge to glass gap that opens up after 35 years of driving.

I applied blue painters tape on vertical trim and on the windshield, leaving a narrow gap. I applied black RTV into the seam and smoothed it flush with my finger. Looks like factory applied. Then did similar to the outer edge with tape on the curved portion of the body as it meet the chrome and on the chrome. Black RTV smoothed and looks great. Similar to how you tape to caulk the bathroom tub. Also stopped the leak.

 

It does leak on both sides but i just had the cowl out a couple of years ago, cleaned all of debris out, and installed a 1/4" mess to keep the leaves out. I plan on removing the cowl again anyway when I do a rain test here soon.